Triblock copolymers containing UCST polypeptide and poly(propylene glycol): Synthesis, thermoresponsive properties, and modification of PVA hydrogel

A series of ABA-type triblock copolymers (PImBF4-b-PPG-b-PImBF4) comprising of poly(propylene glycol) (PPG) as middle block and UCST polypeptide on both sides of PPG was synthesized by ring-opening polymerization of γ-chloropropyl-L-glutamic acid-based N-carboxyanhydride (CPLG-NCA) and then side-chain modification including nucleophilic substitution of the chloro group followed by copper-mediated 1,3-dipolar cycloaddition and subsequent ion-exchange reaction. Variable-temperature UV–vis spectroscopy revealed that the upper critical solution temperature (UCST)-type cloud point temperature (Tcp) was highly dependent on both polypeptide and PPG chain length as well as polymer concentration. Increasing the polymer chain length or concentration frequently results in Tcp increases. Noticeable hysteresis in a cooling/heating cycle was observed for all resulting triblock copolymers owing to a slow disassembly of large aggregates (d = 145 nm) in the heating cycle. Moreover, the resulting UCST triblock copolymers were used to regulate the release property of ciprofloxacin (CIP)-loaded poly(vinyl alcohol) (PVA) hydrogel. The incorporation of PImBF4-b-PPG-b-PImBF4 hampered the burst release of CIP at 37 °C indicating their potential toward sustained release of drug-loaded hydrogels.